Around that time the engineers at GM didn't understand that blower motors do fail, and they had a huge problem with them, especially rumbling from bad bearings, but they didn't design them in such a way that they could be replaced. If you can get to yours by removing a fender, consider yourself lucky. On some models you got a template that showed where to cut about a 12" square out of the firewall sheet metal to get to the motor, then you were to turn that square piece 1/8th of a turn and run sheet metal screws through the four corners to reinstall it. Not a very smart design.